Process for treating iron



Patented Feb. 23, 1926.

UNITED STAT-ES.

PATENT OFFICE;

wm1m,.1. ninnnnrcns AND Anson HAYES, on arms, IOWA. 1

, rnocnss non 'rnna'rmo 1301:.

Ho Drawing. originalapplieatibn filed August 21,1922, Serial No. 588,370. Divided and this am nestion filed August 6, 1925. Serial No. 48,825. a

To all whom it may concern- Be it known that we, WILLIAM J. DIEDER- 10118 and Anson HAYES, citizens of the United States of America, and residents of 5 Ames,Story County, Iowa, have invented a new and useful Process for Treating Iron, of which the following is a specification.

- Thesubject matter of this application was originally included in but has been divided from our 2. plication filed August 21, 1922,-

Serial Num er 583,370.

The object of this invention is to'provide white cast ironwhereby an ironis produced 16 having as great or greater tensile strength than white cast iron and also capable of beg bent and stretched to a considerable degree before breaking. This and other objects of the invent1on 20 will be more clearly pointed out in the specification and claims. a

Any suitable type or form of furnace or so-called annealing oven may be employed ll incar'rying out our improved process, and

' may be heated by any of the well known fuels such as gas, oil or owdered coal burned in connection with air; or the heat may be secured electrically or by acombinaw tion ofcombustionand electricity, or in any other manner that may be desired so long as the desired temperatures and atmospheres are secured. i

The iron'use'd in this process is known as white cast iron, differing principally fromordinary gray iron in that while both contain carbon, the white cast iron contains the carbon principally or wholly in the form of carbid of iron represented by the formula Fe,,O, while gray cast iron contains the carhon to a greater degree in the form of gra bite or graphitic carbon.

T rough t e use of this process we obtain a product having as high or higher'tensile strength than white cast iron and under oertain conditions of procedure also having considerable ductility or ability to bend and stretch, and which is very useful for certain purposes, i i

do not of' necessity pack the white iron castings in boxes or pots containin the packing material, as is done in the or lnary set forth in the appended In carrying out our improved process we malleableizing process asreferred to in our parent application above identified. -.However this may be done at timesif desired, but by omitting it considerable time may be saved. When the packing is omitted the white iron castings may besupported in any suitable manner in the furnace to prevent sagging and warping under the intense heat. a

The process consists in heating for any length of time, raising the temperature of p the white iron castings with convenient a new and improved process for treating rapidity, either rapidly or slowly, to any point between the critical temperature of the material (about 740 degrees centigrade) and the point of incipient fusion, and holding at the chosen high temperature for a period of fifteen minutes to five hours, or-- more. The actual timerequired will depend upon the temperature chosen, lower tem eratures requiring longer times, and upon t e chemical composition of the white iron being treated. In any caseit is only desired to maintain the high temperature until the massive cementite is practically all absorbed in the solid solution. We are satisfied that inmost instances it would avail little to hold at the high temperature for a longer period than about five hours, since practically all of the desirable change would have occurred in that time, especially if the high temperature employed is above 900 degrees centigrade; and that holding for longer periods would resultonly inwaste of time without corresponding benefit. If a bevery materially increased. a l

The castings are then removed from the furnace and cooled by quenchingin any suitable material such as sand, cement, powdered mica or the like, or in any manner outside or inside the furnace, whereby the temperature is reduced to a point considerably below the critical. These operations may then be repeated for any desired 'number of repetitions, that is to say, the material may bealternately heated to a point above the critical temperature and then cooled to a temperature considerably below the critical. The number of repetitions or is used with this fact in mind and should;

. be so construed. I

having a strength of say 50,000 to 85,000 pounds per square inch, or more, with two to eight per cent elongation, or more.

When speaking of the critical temperature ofthe material, the fact should be borne in mind, which is well known in metallurgy, that the critical temperature can be, and is, undercooled by a rapid cooling of the material, and therefore will be reduced by heating to. a tem eratureabove the critical and cooling rapi ly; so that in thereafter heating to the critical temperature, it is obvious that a lower actual temperature willbe involved. The language of this specification and the appended claims w The particular characteristic of the present invention and process, which distinguishes it from another covered by a copending application, is that in the present instance the cooling, after each heatingto a point above the criticaltemperature, is continued until comparativel low temperatures are reached, and such coo ing may be accomplished by any suitable method, eitherinside or out side the furnace, by cooling in any suitable manner such as by quenching or otherwise. .1

As an example of our experiments and to illustrate what we have done, we recite the following: Castings of white iron 7 were heated to 900 degrees Centigrade for seven hours and were then quenched-in oil, after which they were reheated to 700 degrees centigrade for twenty hours, and cooled to room. temperature. -Th s last cooling may be at any desired rate faster than about seven degrees per hour. The product showed a tensile strength of 54,000 pounds per 1 square inch with ten percent elongation, in

two inches.

Likewise by way of illustration. samples of white cast iron were heated to 900 degrees centigrade for five hours, cooled in sand to room temperature, reheated to 810 degrees centigrade and held for one hour then cooled at the rate of two degrees per minute to 650 degrees centigrade. The tensile strength was 72,000 pounds per square inch and elongation six per cent.

Likewise bars of white cast iron were seventeen such beatings the product showed a tensile strength of- 84,700 pounds per square inch with five and one-half per pent elongation in two inches; and after nineteen such heatings the tensile strength was 82,900 pounds per square inch with six per cent elo ation.

We claim as our invention= 1. The process for the heat treatment of castings from white cast iron which consists in 1) subjecting the casting to a temperature above the critical temperature of the material; (2) cooling the castin to a point considerably below the origina critical temperature; (3) reheating the casting to a sufficient temperature to allow structural and chemical changes to progress; and .(4) cooling the casting. y I

2. The process for the heat treatment of castings from white cast iron which consists in (1) subjecting the casting to a tem ature above the critical temperature 0 .the material; (2) cooling the casting to a point considerabl below the originalcritical temperature; 3) reheating the casting to a sutficient temperaturev to allow structural and chemical chan s to progress; (4) coolin the casting; an (5) a repetition of steps (3% and (4) alternate y.

3. The process for the heat treatment of castings from white cast iron which consists in (1) the subjecting of the casting to a temperature above the critical temperature of the material; (2) the cooling of the casting to a point considerably below the ori 'nal critical temperature by quenching; (3 re heating the casting-to asufiicient temperature to allow (structural and chemical changes to progress; (4) cooling to a. temperature sufliciently low that structural and chemical changes cease; and (5) a repetition of steps (3) and (4).

.4. The process for the heat treatment of castings from white cast iron which consists in (1) the subjecting of the casting to a temperature above thecritical temperature of the material; (2) thecooling of the casting to a point considerably below the original critical temperatureby quenching; (3) reheating the castin to a sufiicienttempera- .ture to allow 0 emical and structural from fifteen minutes to five hours, or more, changes cease, at a rate not less than about until the iron carbid gresent is practically seven deegrees centi de per hour. 10

all absorbed in the soli solution, or in other Sign at Des oines, in the county of words until in irons of oommercial compo- Polk and State of Iowa, this 18th day of 5 si'tion the combined carbon is reduced to June, 1925.

substantially nine-tenths of one per cent;

and (2) the cooliniof the casting to a tem- WILLIAM J. DIEDERICHS.

perature where c emical and structural ANSON HAYES. 

